1. Field
The following description relates to a multiple transposition method for superconducting wire, in particular to a multiple transposition method for making each superconducting wire unit from second generation superconducting wires that were firstly transposed and then transposing each superconducting wire unit in such a manner that the phase of each unit can be changed along the length.
2. Description of Related Art
Superconductivity is a phenomenon that electrical resistance becomes zero when temperature, magnetic field or current is maintained below a certain critical value.
In certain materials, electrical resistance vanishes below certain temperature, and these materials allow electricity flow without generating heat, thereby no energy loss occurs. These materials are referred to superconductor, and superconductivity occurs in certain materials and is influenced by temperature, magnetic field and transport current.
Superconductor allows current to flow without resistance only below superconducting transition temperature (Tc) and critical magnetic field (Hc), and For example, critical current density (Jc) exists that is a maximum transport current density whose current is capable of flowing with no resistance. Regarding to the application of the superconductors, it is preferable to manufacture superconductors in the shape of wire or tape, and the manufactured superconductors are being applied to the superconducting electromagnet that generates a high magnetic field.
The coil is produced by winding wires in various geometric shapes, and a magnetic field is generated when current flows through wires. There is no power loss due to resistance if the wire is a superconductor, and this wire is called a superconducting coil.
The superconducting coil or wire is applied to a transformer, a motor, a MRI (Magnetic Resonance Imaging), and a spectroscopy of NMR (Nuclear Magnetic Resonance), and current below critical current, which is a maximum current that keeps superconductivity, must be maintained such that superconductor can be applied to wires of power appliances including superconducting transformer. In case that, in particular, a plurality of superconductor are manufactured in parallel for the large current flow, the sharing of current should be uniform among parallel conductors. If not uniform, a certain conductor from the parallel superconducting conductors exceeds a critical current itself due to the current distribution and thus superconducting wire can be damaged due to the loss of superconducting characteristics.
When coil is manufactured by overlapping several strands of superconducting wires, the balancing of each wire impedance causes the increase of critical current of the whole wires as well as the decrease of AC loss. Therefore, the transposition is very important to prevent the current distribution as to the superconducting wires.
Regarding prior arts of transposition technologies using superconducting wires, there is known “Roebel Bar” from German company, SIMENS. Others are such that the transposition is implemented at the current input terminal after the coils are prepared, and since the second generation superconducting wire substituting for the first generation superconducting wire uses a method for deposition of a superconducting layer on a nickel-alloy substrate, it is hard to carry out a transposition like the “Roebel Bar” method. Moreover, the problems arise that the method for implementing transposition at the current input terminal can hardly implement the transposition if there are many coils, and the benefit of superconducting wires cannot be obtained due to the loss generated by heat at the current input terminal.
Transposition method for superconducting wires shown in FIG. 1 provides a transposition method comprising: preparing a plurality of wires by making curves successively and repeatedly by means of slitting in zigzags on superconducting wires of a thin multiple layer grown epitaxially and then machining the wires with a desired length; and combining the plurality of the prepared wires by superposing curves of wires to come in touch each other.
Also, regarding a process for such superconducting wires, a shearing process, a wire electrical-discharge machining, a press machining, etc. are known.
However, in case that the intensity of electricity required is as high as thousands of to tens of thousands of ampere and thus tens of to hundreds of wires are necessary to consist of transposition wires, the manufacturing of wires by the shear machining or the wire electrical-discharge machining requires that tens of to hundreds of curves should be formed for the transposition and thus wires having tens of to hundreds of meter should be processed. Therefore, during successive process of wires, the productivity decreases sharply and the connection of wires after the machining become worse since the space between curves increases.
Further, in case of the press machining, since the distance in between curves according to the number of wires forming curves for the transposition should be adjusted and thus a mold for a press head should be made in addition, manufacturing cost increases and process for twisting tens of to hundreds of wires together is very complicated, resulting that a productivity decreases and a quality of transposition is deteriorated.